Over the recent past, weighing systems have been developed employing load cells structured in the manner of the so-called "rocker pin". An important advantage realized with this innovation stems from the self-erecting characteristic of the rocker pin configuration. When the normally upright pin is deflected by a horizontally directed force component experienced within the weighing system, it will return to its upright position when the deflecting force terms are removed. A detailed description of such load cells is provided in Dillon, et al., U.S. Pat. No. 4,815,547, issued Mar. 28, 1989, entitled "Load Cell" and assigned in common herewith.
Generally, a number of the rocker pin configured load cells are supported in freely pivotal abutting fashion at their lower end by a ground base through the medium of a receiver component or the like. From this lower contact, the cells extend in vertical columnar fashion to an upper contact surface which, again, is in freely abutting contact with the downwardly disposed surface of a platform or frame having a loading surface adopted to carry the load to be weighed.
The self-erecting feature is developed by configuring the cell or pin component thereof so that the radius of curvature of each end or contact surface is greater than one-half of the total height of the pin. Supported upon such load cell structures, the scale platform and associated horizontal loading surface exhibit several degrees of freedom of movement. Thus it is necessary to accommodate for temporary transverse forces or side loads or lateral forces induced by eccentric loading. For example, when weighing vehicles such as trucks, forward movement and braking, as well as maneuvering during scale entry will be the occasion of acceleration, deceleration, and induced turning moments and the like imposed through the platform in addition to vertical weight force vectors. Typically the extent of lateral travel of the platform is restricted to within small tolerances by bumper structures.
Instrumentation of the rocker pin configured load cells is provided through the media of strain gauges coupled with the columnar or rocker pin components of the structure. This instrumentation may, for example, be protected by employing conventional circuit potting procedures or, may be contained within a protective, sealed, can-like enclosure suspended about the central portion of the rocker pin configured counterforce. Necessary power source inputs to and signal outputs from the enclosed circuitry typically extends through a port or connector connected at the side of the enclosure. Requisite cabling or wiring extends from that connector to power and data gathering systems and the like.
Field experience with these weighing systems has revealed that the temporary transverse or side forces associated by the noted dynamic loads will engender a turning movement in the load cells about the longitudinal or columnar axes of the rocker pin structures. This rotational movement is developed by the somewhat rolling interaction of the contact surfaces of the load cells with an associated support or platform surface. While rocker pin structuring provides for a return to vertical upon removal of transverse loads, the point of contact of such surfaces may vary to evoke a point-to-point progression, the motion of the cells being observed to be somewhat precessional in nature. Particularly where the temporary lateral forces at the weighing platform are bi-directional or, in effect, rotational, this progression of contact point positions, induces turning force vectors within the load cells to promote this rotation. Such rotation can be destructive to any appurtenances extending from the load cells. In this regard, the rotation tends to stress or "wind up" cabling or wiring extending to the load cell instrumentation, causing its breakage with resultant operational loss Necessary repair to the load cells typically involves a substantial labor investment associated, for example, with the jacking up of the platform, the correction of an affected cell and a recalibration of the weighing system. To avoid these encumbrances, a technique is called for which restricts such rotation within acceptable tolerances but which does not affect the dynamic performance of the load cells themselves.